When the number of terminals connecting to one cell in a base station increases over a certain level in a mobile communication system, a processing load increases and thus a minimum performance normally serviced to the connected terminals cannot be guaranteed. To prevent such an overload status, the base station has a function for specifying an allowable connection limit for ensuring the minimum performance of the connected terminals in a cell unit and rejecting a connection request with respect to a connection request exceeding this limit. This function is referred to as call admission control. The call admission control in a multi-user mobile communication system initiates when the terminal initially connects, when an idle terminal requests Radio Resource Control (RRC) connection from a cell, or when a handover to a corresponding cell is requested from another cell.
The base station specifies and has the maximum number of connection allowable connected terminals per cell. Also, the base station counts and has the number of currently connected terminals in every connection and connection release of the terminal. For example, when receiving a terminal's connection request, the base station determines whether a sum of the number of the currently connected terminals and the number of connection requested terminals exceeds the number of the maximum number of the connection allowable connected terminals, accepts the connection and counts the number of the currently connected terminal when not exceeding, and rejects the connection of a corresponding terminal when exceeding.
However, a call connection control method for a conventional mobile communication system does not consider the CA function at all, and thus assumes that one serving cell resource is used per terminal. When the base station supporting the CA function uses the conventional call connection control method while a conventional terminal not supporting the CA and a terminal supporting the CA are mixed, resources of a Medium Access Control (MAC) or Physical (PHY) layer are not properly managed and accordingly a problem arises.
In other words, since there is only one serving cell which manages data transmission and reception per terminal in load calculation for the connection admission control, it was enough for a conventional base station before adopting the CA function to consider only the number of terminals connected to a corresponding cell when calculating the load according to the number of terminals per cell of a base station system. However, although the CA function is adopted, a problem arises when the existing connection admission control function is retained without changing it.
Since resource consumption is considerable due to terminals which add a corresponding cell as a Secondary Cell (SCell) and the load calculation does not consider a resource used as the SCell, a terminal connection requesting the connection as a Primary Cell (PCell) is accepted and an abnormal operation is caused by overloading in MAC/PHY resource processing. Also, when there is a SCell add request for the MAC/PHY resource of a current cell from another cell, there is no means for limiting this.